A two phase liquid-vapor system is normally used in the air conditioning system for automobiles.
Single fluid air conditioning systems with air-to-air heat exchangers, using the reverse Brayton cycle have been proposed for use in automobiles. The U.S. patents to Edwards, Nos. 3,686,893; 3,967,466; and 3,977,852 describe such systems.
In the reverse Brayton cycle refrigeration system, air undergoes an isentropic compression followed by a reversible constant pressure cooling. The high pressure air then undergoes a reversible expansion. The cooled air then picks up heat at a constant pressure and is then returned to the compressor inlet. In the conventional reverse Brayton cycle refrigerating system, heat is not removed during the compression phase of the cycle.